There are many varieties of Musa paradisiaca, the banana tree. The roots are hardy on these tree-like tropicals, but the leaves and trunk can die down to the ground in cold winter weather. Established plants will regrow new tops in the spring after frost has wiped them out. The key here is that it takes 2-3 years for the roots to establish themselves. I'd recommend against planting them in the ground now. If you can take yours indoors this year to protect them, you can plant them in a permanent place in the garden next spring. Then, if the weather cooperates, your trees will become established in another year and should be able to rebound if the winter weather freezes them back. Being in the ground in the very early spring will give the trees a jump-start on their growth spurt. Mature Musa's attain a height of about 20'.